How Can I Quiet-Down Stock Pipe? - '76 175 GP

Currently restoring a '76 175. Would eventually like to use the bike in noise-restricted areas. Any thoughts on how to reduce the "bark" of the stock pipe?

Thanks, all. Binx

You can do a search online for a snorkel. It's a rubber boot to fit over the end of a pipe. I think they may come in different sizes.


http://dirtbike.off-road.com/dirtbike/review/the-db-snorkel-23309.html

You can repack the stock exhaust muffler section which will help. I dont think anyone sells that DB Snorkel anymore but you can do something very similar by cutting an inner tube and clamping a section about 6-8" long that curves the exhaust sound towards the ground. Pointing the sound at the ground disperses it and the rubber of the inner tube absorbs some of the sound. Finally, most people dont realize this but most of the sound from an air cooled two stroke comes from the noise of the ringing air cooled head, a water cooled head dampens all that engine noise and they are significantly quieter. To lower engine noise of an air cooled bike, stuff pieces of rubber in the fins everywhere you can and cut slices of inner tube to wrap around the entire head. I will try to find some pictures of all this. Another thing to do is try to stand so you are between the engine and the sound tester, this works on a Husky because the exhaust and the kicker are both on the left side, when the guy is testing, stand on the left side so you are blocking the sound coming directly from the ringing cylinder.



One last thing, on my Uncle's 76 175 he had a "flapper" on the end of the exhaust which he took off, but it made the bike significantly quieter at the expense of a lot of power. Someone here may have one of those flappers or may know where you can get one.

I would think a new modern silencer would be a great improvement but a bit of custom adapter creation to mount to the frame via rubber parts necessary. Some two stroke sound does not travel all that far if you can have someone else ride the bike and see for yourself. The first stuff I might type has already been mentioned.

A Super Trapp silencer would help Classic versions still available. www.supertrapp.com

Binx, try and look up a pic of a 79 wr 250 my stock cyl. had little rubber pieces between the fins look like rubber hoses. You could try wrapping the expansion chamber with header wrap , they make it in black now too. My 79 wr is to quiet for me really but I think it has a thicker pipe to quiet down the exhaust.

Cut 1/2 inch pieces of fuel line to insert between all fins.
Use large hose clamps to go around a 2/3's circle of rubber fuel line around the pipe...in it's wider section...maybe 2 of them...you want to cut vibration.
Back in the day we also lined the seat-breather airbox with low pile carpet to cut down on intake noise.
That stuff and a good silencer all added up to being able to pass ECEA and (tougher) NETRA enduro sound tests.

Will try the half-inch pieces of fuel line inserted between fins. That's a good, and affordable, place to start.

Not sure I understand the "flapper" concept. I'll look for more info on that. And wrapping the cylinder with slices of inner tube? Would need to see some pics on that. How's that going to affect the air cooling on the cylinder and head?

Is the stock muffler packed with sound absorbing material? Some kind of glass? Haven't had a chance to "fish around" in the stock pipe yet. Maybe a re-pack or over-pack is an easy solution.

Thanks again for all advice. Binx

Heres an older thread on the subject with many suggestions.

http://www.cafehusky.com/threads/ringing-fins-rubber-damping.6292/

Sound is a funny thing. What "sounds" loud does not always "measure" as loud as expected.

Air box noise is definitely a big factor. And try repacking the silencer first. When I had my 1976 175CC I was randomly sound tested at a riding area in Southern California and it passed easily with nothing done except a fairly recently repacked silencer. (Trick with the silencer is not to pack it too tight or too loose.)

I think the California "green sticker" standard for older bikes is and was 101 dBa if that helps to compare to the level you need to meet. (It was a long time ago but I think I was measured in the mid 90 dBa range) Radio Shack used to sell a sound meter that works pretty good or now I believe there are even phone apps that you can use to see if your efforts make a difference.

Crashaholic - great link to the older thread.

Markt2 - what did you use for packing material? I know people have tried a variety of materials but would like to know what worked for you. Buddy of mine is an audio engineer. He should have a line on some cheap decibel-measuring apps for smart phones. Will measure the various fixes to see what does / doesn't have an effect.

Thanks again, guys. Binx

Crashaholic - great link to the older thread.

Markt2 - what did you use for packing material? I know people have tried a variety of materials but would like to know what worked for you. Buddy of mine is an audio engineer. He should have a line on some cheap decibel-measuring apps for smart phones. Will measure the various fixes to see what does / doesn't have an effect.

Thanks again, guys. Binx

The HVA parts list shows your bike came with a dampener strap for the head and rubber fin blocks for the cylinder. Your bike must sing pretty loud if Husky thought this stuff was necessary.

I used the packing they sell for two stroke mufflers... white long-ish strand fiberglass. FMF and others still sell it.

P.S. The rubber straps and blocks on my 175 were missing when I got it... One more thing about that... I remember seeing an old Husqvarna bulletin where in California the CHP would allow a green sticker on the 76 250CR when a "silencing kit" was installed by the dealer. (The 76 CR was MUCH louder than the WR's or your CC). I'm pretty sure that kit was supposed to include the fin dampers, a different muffler, and maybe an intake silencer? These were basically WR parts. I probably found it on this website. Too bad all those tech bulletins seem to be gone.

I found it... apparently I saved a copy! Here's a screenshot of the important part. I'm pretty sure the parts were just off the WR model.
You already should have the "quiet" pipe as the 1976 175CC came with the Skyway silencer built in to the pipe.

What is the built in Skyway silencer and how long was it in use ?